The structural properties of cellular structures have been investigated many years in the past. In addition to the wide variety of uses of cellular structures, there has been developed what is commonly termed a honeycomb structure wherein a generally cellular structure of a wide variety of configurations has been enclosed on open ends thereof with a sheet of material to form a composite structure that has a wide variety of applications. Although there have been proposed certain concepts regarding the continuous production of a honeycomb structure, the optimum in obtaining precision under high speed commercial operations has not heretofore been achieved.
In the manufacture of a cellular structure adaptable for use as a honeycomb core, for example, it is to be realized that two sheets of material are initially adhered together along lines of adhesion and then sliced or sheared into successive strips which are adhered together. The necessary slicing operation incorporates an intermittent operation while the adhesion of material is preferably accomplished continuously. It has been proposed in U.S. Pat. No. 3,035,952 for the entire operation to be performed intermittently, i.e., for the sheets of material to be intermittently moved through gluing and cutting operations. The difficulties and disadvantages of such an approach are believed apparent and, in fact, led to advancements of the sort illustrated in U.S. Pat. Nos. 3,307,440, 3,257,253 and 3,413,177, wherein the gluing or adhesive processing is carried on continuously and the cutting and packing operation is carried on intermittently.
The method and system of the latter patents is disadvantageous in requiring that a slack in the web formed of adhered sheets pile up or be kinked or form waves between some type of overrunning or intermittent feed means and cutting means. For many materials a system of this sort is undesirable as it must be realized that creasing, wrinkling, or otherwise forming flaws in the web of adhered sheets may adversely affect the end product.
An attempt at overcoming the difficulties of the aforementioned system is disclosed in U.S. Pat. No. 3,416,983 wherein a continuous gluing operation is carried out and the resultant web of adhered sheets is fed into an intermittent feed mechanism whereby slack in the web is developed between each cutting operation, and the intermittent feed mechanism removes the slack as the amount of web fed to the cutting mechanism. Such a system suffers from the disadvantage that the amount of web fed into the cutting mechanism for each periodic cutting operation is determined solely by the speed of the continuous gluing operation. It will be appreciated that, for any type of continuous cellular structure manufacture, it is necessary to provide sheets of material to be employed therein in very large quantities. Such quantities can normally be supplied only by rolling sheet material into very large rolls. Any type of drive mechanism withdrawing sheet material from large rolls can only provide minimal web speed control.
Consequently such a system or other prior art systems have been found to feed varying lengths of web formed of adhered sheets into a cutting zone so that successive strips cut from such a web are not of a uniform length (width with reference to the cell structure). The industry has thus become accustomed to the necessity of operating upon a compressed cellular core formed by continuous honeycomb core apparatus as by means of grinding, sanding or the like to produce a uniform core height from successive web strips formed by such apparatus. It will be appreciated that this additional processing is disadvantageous.
The present invention provides for the very precise application of lines of adhesion to sheets forming a web as the web is fed longitudinally in the direction of such lines, and application of adhesion lines to such web which is then precisely cut into identical segments that are adhered to form a compressed cellular structure. Feeding of the web of adhered sheets into a cutting zone is herein controlled entirely by an intermittent feed mechanism substantially without regard to the drive mechanism involved in the application of adhesion lines to the sheets and web of sheets. The foregoing is accomplished by the provision in the present invention of a web reservoir or surge section wherein a substantial length of adhered sheets forming a web ahead of an intermittent drive mechanism feeding the cutting zone, is provided and maintained in the form of a preformed loop with an extension or length greater than the distance from the last means relating to the adhesion process and the intermittent drive means. The length of the loop is substantially in excess of the web length removed by each cutting operation. Consequently the web of adhered sheets is never tensioned by the intermittent drive means which, in turn, then provides the only control over the amount of material of the web fed into the cutting zone for each periodic cutting operation.